This invention relates to a variable valve timing arrangement for an engine and more particularly to an improved arrangement for operating and lubricating such variable valve timing arrangements.
In order to improve engine performance over a wider range of engine speeds and loads, it has been proposed to employ a variable valve timing mechanism (VVT) in the drive for the camshafts of the engine. By varying the phase angle of the camshaft relative to its driving element, it is possible to change the valve timing and, accordingly, make adjustments in valve timing during engine running. In this way, the optimum valve timing can be chosen for each engine running condition.
Conventionally, the variable valve timing mechanism is interposed in the drive between the crankshaft driven element and the camshaft, and generally includes a hydraulically-operated mechanism that is mounted on the end of the camshaft and varies the phase angle at this specific location.
In order to transmit actuating fluid to the variable valve timing mechanism, it has been proposed to provide passages in the bearing arrangement of the engine body for the camshaft which mate with grooves and drilled passageways in the camshaft. Normally, engine lubricant is employed for actuating the variable valve timing mechanism.
It is necessary to obtain close fits in the camshaft and engine body bearing surfaces where these oil supply and return passages are formed. However, it is also desirable or necessary to lubricate the bearing surfaces in this same area. Generally, with prior art constructions, the lubricant is delivered to the camshaft bearing surfaces at a point that is axially spaced away from the valved passages for the variable valve timing mechanism and, accordingly, the camshaft drive system. As a result, there is a cantilevered end of the camshaft which does not receive lubricant. This is obviously undesirable.
It is, therefore, a principle object of this invention to provide an improved variable valve timing mechanism wherein lubricant is supplied to the camshaft surfaces immediately adjacent the variable valve timing mechanism and where the load is the highest.
It is a further object of this invention to provide an improved hydraulic supply, control and lubricating arrangement for the VVT mechanism of an internal combustion engine.